1. Field of the Invention
The present invention relates to a damper mechanism, and more particularly to a damper mechanism for a lockup device.
2. Background Information
A damper mechanism is used, for example, in a power transmission system for transmitting torque while absorbing and damping torsional vibrations. The damper mechanism includes a first rotary member, a second rotary member, and springs or elastic bodies, which will be generally referred to as “elastic members” hereinafter. These elastic members are arranged between the first and second rotary members, and are compressed when relative rotation occurs between these members. The springs may be formed of coil springs. The elastic bodies may be made of rubber or resin. The damper mechanism is employed in a clutch disk assembly, a flywheel assembly or a lockup device of a torque converter, as disclosed, for example, in Japanese Laid-Open Patent Publication No. H8-254246
The elastic members are arranged in windows formed in the first and second rotary members. When relative rotation occurs between the first and second rotary members, the radial ends of the window (i.e., the ends that extend nearly radially on the circumferential ends of the window) circumferentially compress the elastic members. Thereby, the damper mechanism transmits a torque from the first rotary member to the second rotary member, and also operates to absorb and damp torsional vibrations.
In general, each radial end on the circumferential ends of the window has a linear form, and is parallel to a straight line extending between the center of the damper and the circumferential center of the window. When relative rotation occurs between the first and second rotary members, the circumferential end portion of the window moves such that the radially outer portion thereof moves a longer distance than the radially inner portion thereof (see FIG. 4). In FIG. 4, O represents the rotational center of the rotary member, C represents the circumferential center of the window, and θ m represents the angle of relative rotation between the first and second rotary members in a state where the elastic members are compressed to a maximum extent. Thus, the elastic members are compressed by the radial ends of the windows such that the radially outer portion of the elastic members are compressed to a larger extent than the radially inner portion thereof. Accordingly, a larger stress occurs in the radially inner portion of the elastic members due to the larger deformation of the radially outer portions thereof. This reduces the lifetime of the elastic members.
In order to prevent the above situation, the radial ends of the windows are inclined relative to a straight line extending through the center of the damper and the circumferential center of the window so that the window has a substantially trapezoidal form. Thus, the circumferentially opposite ends of the radially outer periphery of the window are respectively located circumferentially outside (i.e., outside in the rotational direction of the damper) with respect to the circumferentially opposite ends of the radially inner periphery. This window shape can suppress an increase in the amount of deformation of the radially outer portion which occurs when the elastic members are compressed.
However, if the radial ends of the windows are inclined excessively, only the radially inner portion of the elastic members will come into contact with a window ends when relative rotation starts between the first and second rotary members, and thus a radially outward force (i.e., a force in a lateral direction of the elastic members) will be applied to the elastic members. If the elastic members have a low rigidity against the radially outward force, they will be deformed. This causes contact between the elastic members and the window ends, and thus increases hysteresis torque and wear on the elastic members.
More particularly, in a lockup device of a hydraulic torque transmission device such as a torque converter, the damper mechanism has been required to have elastic members which have a low rigidity and which allow a large torsional angle for absorbing vibrations. Therefore, elastic members such as coil springs having a larger circumferential length and a lower rigidity have been employed. Therefore, it is thought that that the foregoing problem will be more remarkable in a damper mechanism for a lockup device.
In view of the above, there exists a need for a damper mechanism for a lockup device which overcomes the above mentioned problems in the prior art and which can increase the lifetime of the elastic members used therein. This invention addresses this need in the prior art as well as other needs, which will become apparent to those skilled in the art from this disclosure.